There are various types of gas turbine engine for use in aircraft, but turbofan engines are by far most commonly used in passenger planes and cargo planes. In a turbofan engine, the combustion gas of the gas turbine is expelled rearward and a propeller fan (front fan) provided immediately downstream of the air inlet is driven by the drive shaft of the gas turbine engine. In such a gas turbine engine, a large part of the air drawn into the engine by the front fan is expelled from the rear end of the engine as a propelling airflow while a remaining part of the air is introduced into the combustion chamber of the gas turbine engine as combustion air. In the turbofan engine, combustion gas of high temperature and high pressure is produced by the compressor and the combustion chamber provided in the front end of the engine, and is forwarded to the turbine provided in the rear end of the engine to drive the rotary shaft that integrally carries the impeller of the compressor and front fan. The gas turbine is typically equipped with a compressor of a centrifugal or axial flow type and an annular combustion chamber having a large number of air inlet holes.
In an aircraft gas turbine engine, because the air near the ground is drawn into the air inlet as the aircraft takes off or makes a landing, it is inevitable that the combustion air is mixed with foreign matters. Such foreign matters included in the combustion air may block the air inlet hole of the combustion chamber and/or cause wear to the impeller of the turbine. Therefore, it is desirable to install a countermeasure for removing such foreign matters. A typical arrangement for removing foreign matters in a gas turbine engine consists of a curved passage provided immediately downstream of the diffuser of the centrifugal compressor and a trap port provided in a radially outward part of this passage for removing the foreign matters out of the passage as disclosed in Japanese patent laid open publication No. 2002-242699 (Paragraphs 0017 and 0018, and FIG. 1). In this arrangement for removing foreign matters, the foreign matters trapped by the trap port are stored in a trap chamber, and the engine operator can remove the foreign matters from the trap chamber by removing a plug of the trap chamber when the engine is either not in operation or in operation. It is also possible to provide a solenoid valve instead of the plug to automatically remove the foreign matter while the engine is in operation.